TLR agonists promote ERK-mediated preferential IL-10 production of regulatory dendritic cells (diffDCs), leading to NK-cell activation

Abstract

Regulatory dendritic cells (DCs) play an important role in maintaining peripheral tolerance or immune homeostasis. Our previous study demonstrated that mature DCs could be driven by splenic stroma to proliferate and differentiate into a novel subset of regulatory DCs (diffDCs) displaying a Th2-biased cytokine profile. However, the underlying mechanisms for the unique cytokine profile of diffDCs and how diffDCs regulate the innate and adaptive immunity in response to toll-like receptor (TLR) agonists remain unclear. Here, we report that unlike immature DCs, diffDCs secrete more interleukin 10 (IL-10) but little IL-12p70 in response to lipopolysaccharide (LPS) or other TLR agonists. Up-regulation of extracellular signal-regulated kinase (ERK1/2) activation was shown to be responsible for IL-10 preferential production, and suppression of p38 activation was for impaired IL-12p70 production in diffDCs. Interestingly, LPS treatment could not reverse the inhibitory effect of diffDCs on the proliferation of antigen-specific CD4 ؉ T cells. However, diffDCs could activate natural killer (NK) cells through diffDC-derived IL-10, and even more markedly after stimulation of TLR agonists. These diffDC-activated NK cells could in turn kill surrounding diffDCs. Our results illuminate signal pathways for the unique cytokine profile of diffDCs, and diffDCs can exert their regulatory function even after inflammatory stimuli, thus reflecting one way for strict regulation of immune response. IntroductionDendritic cells (DCs) are the most potent professional antigenpresenting cells (APCs) that integrate a wide array of incoming signals and convey them to lymphocytes, directing the appropriate immune responses. 1 Induction of immune response or tolerance by DCs may be explained by DCs at different developmental stages with different functions, or existence of different subsets of DCs. Immature DCs (imDCs) have been shown to be able to induce tolerance. 2 However, upon inflammatory stimulation or uptake of pathogenic antigens, imDCs migrate to secondary lymph organs undergoing maturation. Mature DCs (maDCs) have a potent immune-stimulatory function by production of cytokines such as interleukin 12 (IL-12) p70, up-regulation of costimulatory molecules, and potent ability to induce Th1 response and activate an antigen-specific CD8 ϩ T-cell response. 3 Recently, subsets of regulatory DCs were identified and considered to be important in maintaining immune homeostasis. [4][5][6] Regulatory DCs negatively regulate immune response by inducing a generation of regulatory T (Treg) cells or a preferential Th2 response. [7][8][9] During investigation of the fate of maDCs after antigen presentation and T-cell activation, we surprisingly found that splenic stromal cells, mimicking the secondary lymph organ microenviroment where maDCs present antigen to lymphocytes, could drive maDCs to proliferate and differentiate into a novel subtype of regulatory DCs (diffDCs), which inhibit rather than activate antigen-specific T-cell proliferation. 10 Compared...

Regulatory T Cells Inhibit Dendritic Cells by Lymphocyte Activation Gene-3 Engagement of MHC Class II

“…ERK was phosphorylated rapidly and transiently upon MHC II cross-linking and its pharmacologic blockade prevented inhibitory responses. ERK activation has been previously associated with inhibition of DCs, IL-10 production, and inhibition of Th1 responses in vivo (37)(38)(39)(40)(41). A dominant role for IL-10 as a mediator of DC suppression after MHC II engagement seems unlikely as there was little evidence in our system for soluble factors.…”

“…Several reports have linked ERK activation with inhibitory signaling and suppression of IL-12 production in DCs (37)(38)(39)(40)(41). ERK was phosphorylated transiently in BMDCs upon MHC II crosslinking, occurring within 5 min after stimulation (Fig.…”

Endocytosis of Mycobacterium tuberculosis Heat Shock Protein 60 Is Required to Induce Interleukin-10 Production in Macrophages*

“…Several studies have highlighted the distinct roles of TLR2 and TLR4 agonists to modulate T cell immune responses by regulating expression of anti-inflammatory and pro-inflammatory cytokines (11,16,19,21,77,78).…”

Splenic Stroma-Educated Regulatory Dendritic Cells Induce Apoptosis of Activated CD4 T Cells via Fas Ligand-Enhanced IFN-γ and Nitric Oxide

“…Proteins were subjected to NaDodSO 4 -PAGE (SDS-PAGE), transferred onto nitrocellulose membranes, and then blotted, as described previously (26).…”